Facsimile and static presentation processing – Static presentation processing – Flying dot
Reexamination Certificate
2000-06-26
2004-08-03
Lamb, Twyler (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Flying dot
C358S001800, C358S001900, C430S124300
Reexamination Certificate
active
06771389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic image formation apparatus, such as an analog copying machine, a digital copying machine, and a printer.
2. Discussion of Background
Conventionally, the following photoconductors are known as electrophotographic photoconductors for use in electrophotographic image formation apparatus:
(1) a single layer photoconductor comprising an electroconductive support
21
and a single photoconductive layer
23
provided on the electroconductive support
21
as schematically shown in
FIG. 3
;
(2) a function-separated type layered photoconductor for use with incoherent writing light, comprising an electro-conductive support
21
, and a layered photoconductive layer comprising a charge generation layer (CGL)
31
and a charge transport layer (CTL)
32
, provided on the electroconductive support
21
as schematically shown in
FIG. 4
; and
(3) a function-separated type layered photoconductor for use with coherent writing light, comprising an electro-conductive support
21
, an undercoat layer (UL)
25
provided on the electroconductive support
21
, and a layered photoconductive layer comprising a charge generation layer (CGL)
31
and a charge transport layer (CTL)
32
, provided on the undercoat layer (UL)
25
as schematically shown in FIG.
5
.
The single layer photoconductor has a simple structure and is inexpensive. However, a sufficiently high photosensitivity for use in practice is difficult to obtain.
The function-separated type layered photoconductor for use with incoherent writing light as shown in
FIG. 4
does not include an undercoat layer (UL) or includes an extremely thin undercoat layer (UL), which is as thin as 1 &mgr;m or less.
The function-separated type layered photoconductor for use with coherent writing light as shown in
FIG. 5
includes an undercoat layer (UL), but the undercoat layer (UL) is still thin.
In the function-separated type layered photoconductor for use with coherent writing light, unless the undercoat layer (UL)
25
is provided, multiple reflections of the coherent writing light is caused between the charge transport layer (CTL)
33
which is the top layer of the photoconductor and the electroconductive layer
21
, and the interference of the coherent writing light subjected to multiple reflections causes uneven photosensitivity in the photoconductor, with the formation of adverse interference fringes in reproduced images. In order to prevent the interference, the undercoat layer (UL)
25
is provided. The thickness of the undercoat layer (UL)
25
is several &mgr;m, preferably 5 &mgr;m or less. The charge transport layer (CTL)
33
usually has a thickness of 20 &mgr;m to 40 &mgr;m.
In comparison with the single layer photoconductor as shown in
FIG. 3
, the function-separated type layered photoconductors as shown in FIG.
4
and
FIG. 5
have a higher photosensitivity and are mainly used in the field of the currently employed organic photoconductors. However, the charge generation layer (CGL)
31
is provided under the charge transport layer (CTL)
33
, so that electric charges generated by the writing light diffuse transversely, repelling each other due to the electric field of each charge in the course of the transfer of the electric charges through the charge transfer layer (CTL)
33
. This causes the formation of blurred latent electrostatic images, and accordingly blurred toner images when developed.
It is considered that a method of reducing the thickness of the CTL to 20 &mgr;m or less, preferably 15 &mgr;m or less could be effective for preventing the formation of such blurred images. However, when the thickness of the CTL is reduced to 20 &mgr;m or less, the electrostatic capacity of the photoconductor becomes so large that a sufficient surface potential for image formation cannot be obtained. This phenomenon becomes conspicuous in particular when the thickness of the CTL is 15 &mgr;m or less. This is because the withstand electrostatic voltage of the CTL is 40 V/&mgr;m to 50 V/&mgr;m, so that the photoconductor should be used at 30 V/&mgr;m or less to be on the safe side. Therefore, it is preferable that a photoconductor with a thickness of 20 &mgr;m be used by being charged to 600 V or less, and with respect to a photoconductor with a thickness of 15 &mgr;m, it is preferable that the charging thereof be 450 V or less. In most image formation apparatus in which a cleaning blade is used for cleaning the photoconductor, the thickness of the photoconductor is generally increased to 30 &mgr;m to 40 &mgr;m with a margin scraped from the surface thereof by the cleaning blade taken into consideration.
The undercoat layer (UL) for use in the conventional photoconductor for use with the coherent writing light can take over a partial voltage of only about 20% of the voltage with which the photoconductor is charged, which partial voltage is not sufficient for preventing the electrostatic breakdown of the photoconductor.
Furthermore, by reducing the thickness of the CTL, there can be prevented the diffusion of electric charges generated within the CGL, which is caused by the mutual repulsion of the electric field of each electric charge in the course of the transfer of the electric charges through the CTL. However, in the case where the thickness of the CTL is merely reduced, the surface potential of the photoconductor decreases if electric charges are applied thereto under the same conditions as in the case where the thickness of the CTL is not reduced, and therefore satisfactory development cannot be carried out by merely reducing the thickness of the CTL. Some conventional photoconductor with such a CTL with a reduced thickness is not capable of clearly reproducing low-contrast thin line images, or utterly unable to produce such line images.
In conventional photoconductors for analog writing, the UL has such a thickness that is sufficient for preventing charge injection from the electroconductive support into the CGL and the CTL, or for making it possible to perform the pretreatment of the electroconductive support for uniformly providing the CGL on the electroconductive support by coating. Therefore, the undercoat layer is extremely thin, with By reducing the thickness of the charge transport layer, there can be prevented the diffusion of electric charges generated within the charge generation layer, which is caused by the mutual repulsion of the electric field of each electric charge in the course of the transfer of the electric charges through the charge transport layer. However, in the case where the thickness of the charge transport layer is reduced, the surface potential of the photoconductor decreases if electric charges are applied thereto under the same conditions, sufficient satisfactory development for use in practice cannot be carried out. Some conventional photoconductor with such a reduced charge transport layer is not capable of clearly reproducing low-contrast thin line images, or completely unable to produce such line images in some cases.
In such conventional photoconductors for analog writing, the undercoat layer has such a thickness that is sufficient for preventing charge injection from the electroconductive support into the charge generation layer or the charge transport layer, or for making it possible to perform pretreatment to the electroconductive support for uniformly coating the CGL on the electroconductive support. Therefore, the UL is extremely thin, with such a thickness that is negligible in comparison with the thickness of the CTL.
Furthermore, even when an LED is used for digital writing, the light from the LED is incoherent light, so that in the function-separated type layered photoconductor for use with the LED, it is unnecessary to cause the UL to have a light scattering function, and therefore, even in this case, the UL has such a thickness that is negligible in comparison with the thickness of the CTL.
In the conventional function-separated type layered photoconductor either for analog writing or digita
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